Optical coherence tomography (OCT) is a technology that allows for non-invasive, cross-sectional optical imaging of biological media with high spatial resolution and high sensitivity. OCT is an extension of low-coherence or white-light interferometry, in which a low temporal coherence light source is utilized to obtain precise localization of reflections internal to a probed structure along an optic axis. In OCT, this technique is extended to enable scanning of the probe beam in the direction perpendicular to the optic axis, building up a two-dimensional reflectivity data set, used to create a cross-sectional gray-scale or false-color image of internal tissue backscatter.
OCT has been applied to imaging of biological tissue in vitro and in vivo, as well as high resolution imaging of transparent tissues, such as ocular tissues. U.S. Pat. No. 5,944,690 provides a system and method for substantially increasing the resolution of OCT and also for increasing the information content of OCT images through coherent signal processing of the OCT interferogram data.
Doppler OCT or Doppler OCT flow imaging is a functional extension of OCT. Doppler OCT (also referred to as Color Doppler OCT) employs low-coherence interferometry to achieve depth-resolved imaging of reflectivity and flow in biological tissues and other turbid media. In Doppler OCT, a scanning optical delay line (ODL) and optical heterodyne detection yield an interferogram with fringe visibility proportional to the electric field amplitude of the light returning from the sample and fringe frequency proportional to the differential phase delay velocity between the interferometer arms. For flow imaging, a variety of processing techniques have been employed to generate estimates of instantaneous fringe frequency. Deviation of fringe frequency from the expected Doppler shift imposed by the ODL can be taken as flow in the sample.
Color Doppler OCT systems continue to improve in sensitivity. Some systems have been developed, which are sensitive enough to flow velocity, such that jitter due to instability of the interferometer components and/or motion of the sample with respect to the OCT interferometer becomes a limiting source of phase noise. In such a case, Doppler shifts of the OCT probe light due to motion of the sample with respect to the OCT interferometer are indistinguishable from Doppler shifts arising from blood flow. In some real-time medical OCT imaging applications, such as retinal imaging, in which the sample is living, sample motion is unavoidable and physical stabilization of the eye, for example, with respect to the interferometer is not practical.
Accordingly, there is a need in the art for an improved device and method for Doppler OCT, which overcomes the above-referenced problems and others.